1. Field of the Invention
The present invention relates to a recording apparatus for recording an image on a recording medium and a recording method.
The recording apparatus includes, e.g., those in the form of a facsimile apparatus, an electronic typewriter, a copying machine, a printer apparatus, and the like.
2. Related Background Art
In general, a thermal transfer printer employs an ink sheet in which a hot melt (or thermal sublimation) ink is coated on a base film. The ink sheet is selectively heated by a thermal head in accordance with an image signal, and a melted (or sublimated) ink is transferred onto a recording sheet, thereby performing image recording. In a thermal transfer recording system, a time interval between recording operations for two adjacent lines is often prolonged. In this case, in order to prevent the thermal head from being completely cooled, so-called auxiliary recording is proposed. That is, the thermal head is heated so as not to perform transfer recording while recording data of the thermal head remains the same. The auxiliary recording will be described below with reference to FIG. 7.
FIG. 7 shows image recording timings for a line type thermal head. Timings T101 to T104 correspond to output timings of a print command for instructing start of printing and trigger timings of a recording sheet convey motor. In FIG. 7, timings 70 to 73 indicate actual recording timings for one line. During this interval, a recording sheet is conveyed by one line, and one-line recording is performed. As indicated by the timings 71 and 72, when recording for the next line is instructed during recording for the present line, recording processing for the next line is started immediately after recording for the present line is completed. However, when a recording interval must be set until recording for the next line, auxiliary recording operations are executed, as indicated by timings 74 to 76.
In the above-mentioned prior art, however, when the recording interval is prolonged, the auxiliary recording is spoiled, and heat of the thermal head is dissipated. As a result, a recording density for the next line may be decreased. In particular, when lines are intermittently recorded in, e.g., a facsimile apparatus, a rising time of a heating operation of the thermal head is delayed, and white stripes due to an insufficient image density may appear in a recorded image.
On the other hand, a thermal transfer printer employs an ink sheet in which a hot melt (or thermal sublimation) ink is coated on a base film. The ink sheet is selectively heated by a thermal head in accordance with an image signal, and a melted (or sublimated) ink is transferred onto a recording sheet, thereby performing image recording. Since an ink of the ink sheet is normally completely transferred to a recording sheet by a single image recording operation (i.e., a so-called one-time sheet), the ink sheet is conveyed by a length corresponding to a recording length after recording of one character or one line is completed, and the unused portion of the ink sheet must be reliably conveyed to the next recording position. For this reason, an amount of use of the ink sheet is increased, and running cost of the thermal transfer printer tends to be higher than that of a conventional thermal printer for recording an image on a heat sensitive sheet.
In order to solve this problem, as disclosed in U.S. Pat. No. 4,456,392, Japanese Laid-Open Patent Application No. 58-201686, and Japanese Patent Publication No. 62-58917, a thermal transfer printer which conveys a recording sheet and an ink sheet to have a speed difference therebetween is proposed.
The present invention has been made in view of the inventions described in these prior arts. As described in these prior arts, an ink sheet which can perform an image recording operation a plurality of (n) times (so-called multi-print sheet) is known. When an image is recorded over a recording length L using this ink sheet, a convey length of the ink sheet conveyed upon completion of or during image recording can be smaller than the length L (L/n : n&gt;1). Thus, a use efficiency of the ink sheet can be n times that of a conventional apparatus, and a decrease in running cost of a thermal transfer printer can be expected. This recording method will be referred to as a multi-print method hereinafter.
In multi-print recording using such an ink sheet, an ink in an ink layer of the ink sheet is separately heated n times. In each heating, a shearing force is generated between a melted (or sublimated) ink and a non-melted (or non-sublimated) ink, thereby transferring ink onto the recording sheet. For this reason, when a time until recording for the next line is prolonged after recording for a certain line and an ink temperature is decreased, the shearing force between the melted and non-melted ink portions is increased, and the ink sheet and the recording sheet are not easily separated from each other. This phenomenon typically occurs when one-line recording data includes much black information, and poses a serious problem when a time interval between the present line and the next line is not constant and is relatively long.
The present applicant proposed a thermal transfer recording apparatus and a facsimile apparatus using the same (Japanese Patent Application No. 63-281375 filed on Nov. 9, 1988). In this apparatus, when identical data is recorded while a recording medium stands still, and a recording operation is interrupted for a predetermined period of time or more, a recording means is heated until the next recording operation to improve quality of a recorded image, and to facilitate separation between of the ink sheet and recording medium.
The present invention is made by further developing the above invention.